Switching power supplies are popular for high power applications because of their high efficiency and the small amount of area/volume they require. Popular switching supply topologies include buck, boost, buck-boost, forward, flyback, half-bridge, full-bridge, and SEPIC topologies. Buck converters are particularly well suited for providing the high current at low voltages needed by high performance integrated circuits, such as microprocessors, graphics processors, and network processors.
Power consumption and thermal management are major issues in modem computer systems. In systems with many processors, some of the processors are often in idle or less than full power states. When the processors are in this low power state, the power consumption of the power supply may be reduced to minimize the total system power consumption and dissipation.
One drawback to multiphase regulators, such as buck DC-DC converters, is that considerable power is used during light load conditions to switch the multiple buck conversion phases. As a result, the efficiency of multiphase converters can be poor at light loads. In addition, as more phases are added to improve full load efficiency, the light load efficiency decreases. The most efficiency sensitive applications often use more phases to improve the full load efficiency, but sacrifice medium load and light load efficiency. In many applications, processors spend a majority of the time operating in the medium load range and only use peak load current for short durations. Systems are consequently over designed, resulting in higher costs for cooling, AC-DC power supplies, and AC power used.
At medium and lighter loads, fewer phases may be used to provide the load current. Fewer active phases makes a converter more efficient at the typical processor load currents. One problem is that modern processors can change the load demand very quickly (within microseconds) so that the converter must respond to this change in current without an overload (too much current) condition in any of the phases.
In multiphase controllers, phase dropping (aka phase shedding) and phase adding have been implemented in a variety of ways. Multiple methods exist for determining when to drop or add phases for optimum efficiency. Typically, dropping or adding phases is done without regard to the timing of the switch mode regulator. This can result in large temporary voltage variations, often referred to as glitches, at the output of the regulator.